This invention relates to a cathode ray tube having an envelope containing electrically operable components comprising at least means for producing an electron beam and flexible conductor means extending between leadthrough means in the wall of the envelope and terminals of the electrically operable components for supplying power thereto, and wherein the conductor means comprises a flexible circuit of at least one film of insulative material on which a plurality of conductive tracks are provided.
Such a cathode ray tube is the subject of British Patent Application No. 8521580 as yet unpublished. The use of a flexible circuit as the conductor means has considerable advantages over conventional discrete wires employed previously as conductor means. The flexible circuit, being thin, occupies very little space in one plane and can easily be routed around the internal structure of the tube. This is particularly advantageous in the case of a flat type of cathode ray tube as described in the aforementioned patent application where internal space is, in view of the nature of the tube, at a premium and in which a comparatively large number of electrically operable components are present in the envelope. Further, as the supply conductors are constituted by conductive tracks, for example thick film tracks, carried on the film, assembly of the tube is greatly facilitated in comparison with the use of conventional separate wires. As is also described in British Patent Application No. 8521580, the flexible circuit may comprise a plurality of films each carrying a number of thick film conductive tracks, the plurality of films being stacked and secured together forming a film assembly. Because each film is flexible and relatively thin, such an assembly of track-carrying films is still comparatively thin and highly flexible and so the advantages discussed above are retained.
Polyimide material is used for the film(s). The thick film conductive tracks are deposited directly on the polyimide film(s), for example using screen printing techniques, and terminations provided at each end of the flexible circuit for connection with pins of the leadthrough means on the one and terminals associated with the internal, electrically operable, components on the other. This construction presents little or no outgassing problems.
This type of conductor means interconnecting the leadthrough means and terminals of internal components has been found to work very well generally. However, where particularly high electrical currents are to be supplied to a certain component, for example an electron gun heater, problems might be experienced and the high currents involved could perhaps lead occasionally to breakdown of the conductive thick film track or tracks concerned.
It is an object of the present invention to provide an improved form of flexible circuit conductor means which can reliably handle the relatively high currents supplied to, for example, an electron gun heater.